Edited by Shiloh - 7/3/12 at 4:48pm
I don't really have an answer other than wait and see, but from personal experience, I usually have 3-4 days of fertile CM before I actually ovulate, so if you DTD CD12, then didn't ovulate until day 16 or 17, you are probably fine.
I wasn't checking my cv regularly before
how long had your IUD been in place?
My period is due tomorrow, tests still negative.
I would guess that the level of hormone secreted by the IUD would have made your endometrial lining unreceptive to an egg this month.
My Mirena fell out too, but I never really got regular periods while on it. Your cycle probably wasn't regular? About 2 months after mine came out (I had it in starting 6 weeks postpartum, then for about 1.5 years) my periods came back and were perfectly on schedule.